Add roast and carrots to slow cooker. Thinly slice onion and mince the shallot. Combine the onions, shallot, salt, pepper, oil, vinegar, tomato juice, broth, thyme, bay leaves, cumin and garlic powder; pour over roast. Cook on low for 8 hours.
Remove roast and veggies from crockpot. Whisk together cornstarch and water. Add to a small saucepan with juices from the roast. Heat on low, whisking constantly until sauce thickens.
Cook rice before serving, as directed on package.
Serve roast with sauce on top with carrots, rice and pineapple on the side.